Who will walk me down the aisle!?!

Walk with whoever you want. It's your decision, no one else's. If your mother's family hates this person that much, maybe they are the ones who don't need to attend because no one needs to deal with toxicity at what should be a happy event.

I will probably ask a close friend to walk me down the aisle. I have too much anxiety to walk myself and I know for a fact that if I don't have an escort, I will be frozen in place and unable to move on my own due to nerves, which is actually a very natural reaction.

There is no "giving away" symbolism by anyone nor has there been for centuries outside of the movies.

What about your mother walking you down the aisle? There’s no reason it has to be a male who does it. I can see walking with your 20 month old would be cute, but personally I’d be worried about so young a child.

The "it's my day" thing doesn't work when we are talking about courtesy and comfort to guests (e.g., having enough seats, climate controlled reception, serving enough food appropriate to the time of day). But THIS is absolutely, 100% completely your decision. The word "traditional" is pretty irrelevant here, since these traditions vary widely by country/region, religion, social class, and time period.

Who walks with you down the aisle doesn't really impact other people, no matter how much they try to convince you it does. If you want to walk with your son, do it. If you'd prefer to walk alone, do it. If you want to invite your "stepdad", do it. Make your decision and then just stop discussing it with other people.